Conventionally, in an image forming apparatus, immediately after power is turned on or at the time of recovery from sleep state, image quality maintenance control and alignment control are executed in order to stabilize image quality. The image quality maintenance control and the alignment control consume toner of all the colors of yellow, magenta, cyan and black. Therefore, as the image quality maintenance control and the like is carried out many times, the quantity of toner in a developing device is reduced. Moreover, in the present status, toner is not supplied to the developing device when the image quality maintenance control and the alignment control are carried out.
For the conventional image forming apparatus, there are two mechanisms for supplying toner to the developing device, that is, (1) toner supply during ordinary printing and (2) toner supply when carrying out toner refreshing.
The toner refreshing is originally prepared for maintaining stabilization of image quality when carrying out image formation using color toner. Therefore, the startup of the toner refreshing is determined when the number of print sheets in the image formation using color toner exceeds a predetermined number of sheets. If it is determined that the print rate of at least one color of yellow, magenta, cyan and black is low, the toner refreshing is executed with respect to the developing devices of all the colors. In this case, toner is supplied to a developing device which is determined as having insufficient toner.
However, if the user only uses monochrome print, the quantity of remaining toner in the yellow, magenta and cyan developing devices is not grasped, though the quantity of remaining toner in the black developing device is monitored.
Thus, in the state of use where only monochrome print is mainly used, the toner refreshing is not executed and therefore the toner in the developing devices is reduced by the toner consumption due to the image quality maintenance control and the alignment control. Consequently, the image quality maintenance control and the alignment control cannot be carried out in some cases.